Tungsten filament iodine cycle incandescent lamp with alkali metal getter



' Dec. 10, 1968 D w MAYER 3,416,022

TUNGSTEN FILAMEN'i' IdnINE CYCLE I-NCANDESCENT LAMP WITH ALKALI METAL GETTER Filed Feb. 24, 1965 INVENTOR 00mm IVA/Wm BY mm M,

ATTORNEYS United States Patent 3,416,022 TUNGSTEN FILAMENT IODINE CYCLE INCANDESCENT LAMP WITH ALKALI METAL GETTER Donald W. Mayer, New Market, N.J., assignor, by mesne assignments, to Wagner Electric Corporation, South Bend, Ind., a corporation of Delaware Filed Feb. 24, 1965, Ser. No. 434,901 7 Claims. (Cl. 313-178) ABSTRACT OF THE DISCLOSURE A small quantity of an alkali metal iodide, e.g. sodium iodide, is placed within the envelope of a tungsten filament lamp during manufacture of the lamp. When the filament is first heated by passage of electric current therethrough, the alkali metal iodide is vaporized to provide iodine gas for maintaining the tungsten-iodine regenerative cycle and free alkali metal as a getter for water vapor, oxygen, and like impurities in the lamp.

This invention relates to a tungsten lamp having a tungsten filament within an envelope which contains gas at a reduced pressure. When the lamp is first fabricated, a compound containing iodine and an element which will act as a getter is introduced into the envelope and positioned on the filament. When the compound is disassociated by the action of the high temperature furnished by the filament, the iodine is vaporized and the getter is deposited on the envelope walls. During the time the lamp is in operation, the iodine vapor collects the evaporated tungsten and deposits it on the filament. The getter substance combines with water vapor, oxygen, and other unwanted gases to maintain the atmosphere within the envelope in a pure operating condition.

The iodine tungsten lamp is well known and has been in use for some time. Because of the iodine vapor within the lamp envelope, the tungsten filament can be raised to a much higher temperature than was possible with prior lamps using only argon as a gas filler. However, the injection of iodine into the lamp envelope requires considerable skill and the use of additional fabricating equipment which was not necessary with ordinary lamps. The present invention eliminates these extra precautions and reduces the cost of manufacture by simply placing a small quantity of sodium iodide on the filament when the lamp is first made. Since sodium iodide is a solid, it can be handled easily and its weight can be controlled within a narrow range. The lamp may be processed in the usual manner, provided with an inert gas filling, and sealed. After sealing, the tungsten is heated by the passage of current, the sodium iodide is disassociated and the lamp is ready for use.

One of the objects of this invention is to provide an improved tungsten iodine lamp which avoids one or more of the disadvantages and limitations of prior art lamps.

Another object of the invention is to permit faster and easier manufacture of high efiiciency lamps.

Another object of the invention is to lengthen the life of tungsten lamps by providing an efficient getter as well as a small quantity of iodine.

Another object of the invention is to increase the efficiency of iodine vapor tungsten lamps by the provision of a getter which is always ready to absorb water vapor.

Another object of the invention is to reduce the cost of manufacture of tungsten lamps and to reduce the amount of equipment necessary for the lamps fabrication.

3,416,022 Patented Dec. 10, 1968 The invention comprises a tungsten iodine lamp having a sealed envelope which contains a tungsten wire with lead-in conductors for connection to a source 01 electric power. An inert gas is sealed within the envelope at a pressure which is within the range of one-half to six atmospheres. A quantity of an iodide, such as sodium iodide, is disposed on the tungsten wire when the lamp is first manufactured. When the lamp is heated for the first time by the passage of current through the filament, the sodium iodide is disassociated into iodine and sodium, the sodium providing a getter material for absorbing unwanted gas impurities.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing.

FIG. 1 is a cross sectional view of the lamp taken along its axis and showing the envelope, a helical tungsten filament, and a small quantity of an iodine salt.

FIG. 2 is a cross sectional view of the lamp shown in FIG. 1 and is taken along line 22 of that figure.

Referring now to the drawing, the lamp includes a cylindrical envelope 10 which is preferably made of quartz but may be made of any similar transparent glass substance which is able to withstand high temperatures. A tungsten filament 11 is positioned within the lamp disposed along the axis of the cylindrical envelope. The tungsten filament may be wound in a small helix as shown in FIG. 1 or may be a straight wire. At either end of the filament, a lead-in conductor 12 is secured in an envelope seal 13. The tungsten filament is welded or otherwise secured to the internal ends of these conductors for the transfer of electric power.

When the filament is assembled, a small quantity of sodium iodide 14 is placed on the filament. This chemical combination is a solid and is generally obtainable as a powder. It may be mixed with water or some other suit able liquid to act as a binder during the time the envelope is being exhausted and filled. As is well known, these lamps give the best performance when they are filled with an inert gas such as argon or krypton. The pressure depends upon the future performance of the lamp and may be within the range of one-half atmosphere to six atmospheres.

Extensive tests have shown that sodium iodide works well as a compound which increases the efficiency of the lamp and which also furnishes an efiicient getter. However, other types of iodide can be used such as potassium iodide.

In one example, a quartz cylinder having about five cubic centimeters internal volume was sealed with a tungsten filament as shown in FIGS. 1 and 2. A quantity of sodium iodide was deposited on the filament having a weight of 0.6 milligram. Then the lamp was filled with a mixture of argon (88%) and nitrogen (12%), the pressure at room temperature being 600 millimeters of mercury. After sealing off, sufficient current was supplied to the lamp to heat the tungsten wire to about 2600 centigrade. Within one minute of the initial passage of current, all the sodium iodide was disassociated and the lamp was in its desired operating condition.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and .are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. A tungsten iodine lamp comprising, a transparent sealed envelope, a tungsten wire placed within the envelope, an inert gas also within the envelope, a quantity of an alkali metal iodide disposed on the tungsten wire in an amount effective to provide, upon vaporization of said iodide when the tungsten wire is first heated by the passage of electric current therethrough, iodine gas for maintaining the tungsten-iodine regenerative cycle and free alkali metal as a getter for any water vapor, oxygen, and like impurities present in the lamp.

2. A tungsten iodine lamp as claimed in claim 1 wherein said alkali metal iodide is sodium iodide.

3. A tungsten iodine lamp as claimed in claim 1 wherein said alkali metal iodide is potassium iodide.

4. A tungsten iodide lamp comprising, a transparent sealed envelope of quartz, a tungsten wire within the envelope, lead-in wires sealed in the envelope wall for connection to a source of electric power, an inert gas within the envelope, a quantity of alkali metal iodide disposed on the tungsten wire in an amount effective to provide, upon vaporization of said iodide when the tungsten wire is first heated to a temperature above 2000 C. by passage of electric current through the leadin wires and the tungsten wire, iodine gas for maintaining the tungsten-iodine regenerative cycle and free alkali metal as a getter for any Water vapor, oxygen, and like impurities present in the lamp.

5. A tungsten iodine lamp as claimed in claim 4 wherein the inert gas within the envelope is composed of substantially 88% argon and 12% nitrogen, at a pressure which is substantially 600 millimeters of mercury at 22 centigrade.

6. A tungsten iodine lamp as claimed in claim 4 wherein the tungsten wire is wound in an open helix and wherein the envelope is cylindrical having an internal diameter of not more than five times the external diameter of the helix.

7. A tungsten iodine lamp as claimed in claim 4 wherein said alkali metal iodide is sodium iodide.

References Cited UNITED STATES PATENTS 3,189,395 6/1965 Demas 313-227 X 1,025,932 5/1912 Steinmetz 313-225 X 1,925,857 9/1933 Van Liempt 313-222 X 2,073,715 3/1937 Stone et al. 313-174 X 3,091,718 5/1963 Shurgan 313-222 3,132,278 5/1964 Collins et al. 313-178 2,173,258 9/1939 Lederer 313-180 X FOREIGN PATENTS 734,956 8/1955 Great Britain. 952,939 3/ 1964 Great Britain.

JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Primary Examiner.

US. Cl. X.R. 

